The present invention relates to generators and, more particularly, to an enclosure for a generator rotor.
In a conventional generator having a rotor and a stator, the rotor is provided with field windings that excite the generator while receiving a current from an exciting current source. The stator is provided with armature windings from which electrical power is output. Typical rotor construction requires that a field winding be assembled, bar by bar, into radial slots milled into a rotor forging. Containment of the rotor field windings is typically achieved using rotor wedges, rotor teeth and retaining rings.
In commonly owned U.S. Pat. No. 6,239,527, an enclosure for a rotor in a generator is described that is constructed of a non-magnetic, and preferably filament wound tube. The '527 patent discloses that the enclosure may be formed as a continuous tube or as a plurality of rings, preferably slightly oval in shape.
In commonly owned U.S. Pat. No. 6,291,919, a metal enclosure shield is disposed between the non-magnetic enclosure and the winding assemblies on the rotor. The enclosure shield is constructed of an electrically conductive material such as aluminum and is designed to provide adequate electromagnetic shielding for the rotor field winding, with good electrical contact with the magnetic core poles, while also providing axial stiffness to the winding structure. However, the insertion of a metallic shield radially between the composite enclosure and the field winding as described in the '919 patent is not a satisfactory solution in light of, for example, structural and manufacturing issues relating to stress concentration.
In commonly owned U.S. Pat. No. 6,495,942, the rotor enclosure is preferably constructed from a low density composite material such as a carbon fiber-glass fiber composite material.
Graphite epoxy based composite laminates have significant specific strength (strength-to-density ratio) compared to metallic material. However, graphite laminates have low interlaminar shear strength and the inplane tensile strength of the composite is very sensitive to surface damage that severs fibers. Thus, the use of graphite laminates as structural components in a rotating stress field (such as a rotor structural enclosure) is technologically problematic.
Moreover, when graphite (carbon fiber) composite interfaces with a conductive metallic component, such as an aluminum alloy, Galvanic interaction and resulting corrosion is likely to occur.